Drainage-independent genetic structure and high genetic diversity of endangered freshwater pearl mussels (Margaritifera margaritifera) in northern Europe

Abstract

Freshwater pearl mussels (Margaritifera margaritifera) are among the most critically threatened bivalve molluscs worldwide. An understanding of spatial patterns of genetic diversity is crucial for the development of integrative conservation strategies. We used microsatellites to study the genetic diversity and differentiation of 14 populations of M. margaritifera in central Sweden, an area which was described as a major secondary contact zone in postglacial colonisation for other species. Genetic diversity of Swedish pearl mussel populations was much greater than in central and southern Europe but similar to the genetic diversity observed in the northeastern portion of their European range. Genetic differentiation among populations was pronounced but to a large extent independent from present-day drainage systems. The complex patterns of genetic diversity and differentiation in pearl mussel seem to be strongly influenced by the species' high degree of specialisation and extraordinary life history strategy which involves facultative hermaphrodism and an obligatory encystment stage on a host fish. Genetic drift effects and anthropogenic disturbances resulting in reduction of population size and loss of connectivity are less pronounced in northern pearl mussel populations compared to those in central and southern Europe.

Lifting the curtain on the freshwater mussel diversity of the Italian Peninsula and Croatian Adriatic coast

“…Although the majority of published studies on freshwater mussels have evaluated genetic diversity based mainly on partial distributions (e.g. Nagel et al 1996;Machordom et al 2003;Araujo et al 2005Araujo et al , 2009Geist et al 2010;Prié and Puillandre 2014), recent ones have included detailed phylogeographic data covering entire species ranges (Froufe et al , 2016a. These studies highlighted Iberia, North Africa and the Balkans as primary refugia, in accordance with what has been described for the majority of other taxa (e.g.…”

Strategies for the conservation of endangered freshwater pearl mussels (Margaritifera margaritifera L.): a synthesis of Conservation Genetics and Ecology

“…The same study revealed a close relation of specimens from both sides of the Atlantic. In contrast to allozyme and mitochondrial variability, analyses of microsatellites revealed high degrees of population structure and very different levels of genetic diversity among European populations (Geist et al, 2003;Geist & Kuehn, 2005;Bouza et al, 2007;Geist et al, 2009). Genetic variability as measured by allelic richness and heterozygosity levels appears to be the highest in the north-east of the species distribution range which can be explained by the species life history strategy and by the lesser extent of habitat destruction in these areas .…”

“…Petit et al, 1998). Based on a comparison of the heterozygosity contribution of individual populations to average heterozygosity levels, genetically determined priority populations for conservation have been identified for pearl mussels and for their host fishes in different geographical regions (Geist & Kuehn, 2005Geist et al, 2009).…”

Captive breeding of the endangered freshwater pearl mussel Margaritifera margaritifera

“…In common with other freshwater mussels (Berg et al 2007, Elderkin et al 2007, Zanatta & Murphy 2007, M. margaritifera shows a significant degree of population structuring (Machordom et al 2003), even at small spatial scales (Geist & Kuehn 2005, Bouza et al 2007. Areas colonised by M. margaritifera since the last glacial maxima display high genetic diversity (Geist & Kuehn 2008, Geist et al 2009, and this may be indica-tive of locally adapted populations, as seen in their salmonid hosts (Garcia de Leaniz et al 2007), and should be taken into account when developing ex situ conservation programmes for the species (Geist & Kuehn 2005). For example, translocations of mussels between watersheds or introduction of artificially reared individuals may result in gene introgression and the breakdown of local adaptations, further compromising the conservation of depleted populations.…”